Currently there are many aircraft engine parts produced which have a large number of small holes for delivery of cooling air to protect the subject part from high temperature damage. In most cases, such parts have a hole size referenced on the drawing but the acceptance criteria is air flow (air passed through the subject holes per unit time). Because of the number of holes normally found in such parts and the required uniformity of air distribution, the tolerance on hole size is quite small. Many times such holes are undersized, or as specified, and do not deliver the required air flow. In such cases, the options for increasing hole size are limited and expensive.
Several approaches that have been used in the past are to process the holes through a re-drill operation at the high risk of generating scrap since locating and maintaining the exact centerline of the hole during re-drilling on many hundreds of holes is nearly impossible.
Another approach is to abrasive flow machine the holes. However, because the carrier has high resistance to flow, abrasive particles at the media-hole wall interface will remain at the surface. This results in material removal at both the peaks and valleys by the grinding action of the abrasives. Further disadvantages of this method include limited abrasive particles per unit time, considerable tooling cost, processing time, and in some cases destruction of parts due to distortion because of the high pressures required to move the process media (a putty-like substance containing abrasive particles) through the small holes.
These existing processes are expensive, time consuming, and have a high probability of causing the part to be scrapped.
It would be desirable, then, to be able to apply an improved abrasive hole polishing system which is not subject to the foregoing disadvantages. The objects, features and advantages of the present invention will become more readily apparent in the following description when taken in conjunction with the appended drawings.